Some new designs of mobile communication devices—such as smart phones, tablet computers, and laptop computers—include two or more radio access technologies (“RATs”) that enable the devices to connect to two or more radio access networks. Examples of radio access networks include LTE, GSM, TD-SCDMA, CDMA2000, and WCDMA. Such mobile communication devices (sometimes referred to as “multi-RAT communication devices”) may also include one or more radio-frequency (RF) communication circuits or “RF resources” to provide users with access to separate networks via the two or more RATs.
Multi-RAT communication devices may include mobile communication devices (i.e., multi-Subscriber-Identity-Module (SIM), multi-active or “MSMA” communication devices) with a plurality of SIM cards that are each associated with a different RAT and utilize a different RF resource to connect to a separate mobile telephony network. Multi-RAT communication devices may also include multi-SIM-multi-standby or “MSMS” communication devices, which individually include two or more SIM cards/subscriptions that are each associated with a separate RAT, and the separate RATs share one or more RF chains to communicate with a plurality of separate mobile telephony networks on behalf of their respective subscriptions. Further, multi-RAT communication devices may include single-SIM communication devices, such as single-radio LTE (“SRLTE”) or simultaneous GSM+LTE (“SGLTE”) communication devices, which individually include one SIM card/subscription associated with two RATs that share a single shared RF resource to connect to two separate mobile networks on behalf of the one subscription.
Typically, a conventional multi-RAT communication device includes a crystal oscillator used, among other things, to provide a stable clock signal for digital integrated circuits and to stabilize frequencies for radio transmitters and receivers used by each RAT on the device to enable a RAT to communicate with a base station. When stabilizing frequencies, the multi-RAT communication device generally performs adjustments to the operational frequency of the crystal oscillator to account for the base station's natural deviations from its expected/standard frequency or timing (i.e., sometimes collectively referred to as the base station's “frequency error(s)”). For example, in response to determining the frequency error for a RAT's base station, the multi-RAT communication device may adjust its crystal oscillator's frequency to account for the determined frequency error of the base station, thereby enabling the RAT to acquire/maintain service with the base station using the corrected frequency.
Currently, RATs on a multi-RAT communication device may individually communicate with numerous different base stations. In conventional networks, timing mechanisms/clocks of base stations within the same network are usually synchronized to ensure consistent service for devices on that network, and as a result, these intra-network base stations usually have similar frequency errors. However, base stations associated with different networks or services providers typically do not have comparable frequency errors because separate networks usually are not synchronized with each other. Further, in some rare circumstances, it may also be possible that base stations within the same network have dissimilar frequency errors for various reasons, such as aging frequency generating components on some of the base stations.
Because a multi-RAT communication device must account for frequency errors of a variety of different base stations/networks to enable each of the multiple RATs to communicate with and/or receive service from their respective base stations, the potential differences in frequency errors between different base stations currently present a design and operational challenge for multi-RAT communication devices.